The present invention relates to an endoprosthesis percutaneously implantable by means of a catheter in the body of a patient, particularly in tubular vessels or organs, said endoprosthesis being designed in the form of an oblong, hollow body and, upon placement in the correct position during implantation, being changeable from a small lumen during insertion into a larger lumen conforming to its functional position.
Prostheses capable of being inserted percutaneously and changeable in their lumen are known. They serve the purpose of opening or widening vascular lumina either by mechanical expansion by means of known balloon catheters from a small to a larger lumen, or such a prosthesis expands by itself after prior compression by spring force prior to the implantation, due to the initial stress produced in the spring during the compression.
EP 0,292,587 describes an endoprosthesis that is received on a balloon catheter and expandable by dilation, as well as detachable from the catheter and placed in a vessel. This prosthesis is a xe2x80x9cstentxe2x80x9d manufactured by knitting or crocheting from metal or plastic thread material into the form of a hose-like hollow body, in connection with which the individual stitches consist of loosely meshing loops. During expansion, widening, due to dilation of the balloon of the catheter, the meshing loops undergo plastic deformation, and the expanded prosthesis thus remains in its expanded position.
Self-expanding stents have been described in the prior art, for example in EP-A-0,183,372, U.S. Pat. No. 4,732,152 and DE-OS 4,137,857. Prior to their implantatio n, these prostheses are compressed against inherent spring return forces to a reduced cross section, inserted into the body in the compressed state, and, upon placement in the correct position, expand again in the respective vessel or hollow body of the patient""s body due to cancellation of the force of retention, and are fixed thereby.
The endoprosthesis described in EP-A-0,183,372 is one which, for the purpose of implantation, is compressed to a reduced cross section and then pushed in the compressed state by means of a pusher through a catheter previously inserted in the vessel, until it is positioned in the right position in the vessel. Such advancing of the prosthesis through the catheter requires a considerable expenditure of force because the displacement is counteracted by high frictional forces.
A woven and elastically designed endoprosthesis has been described earlier in U.S. Pat. No. 4,732,152, which, in the compressed state, is kept together by a double cover, which is closed at the distal end. This cover is pulled back from the folded prosthesis in the same way as a stocking is pulled from the foot of a wearer. For the purpose of avoiding the friction occurring in this process, liquid may be filled in between the two leaves of the cover. However, this system, which seems to be initially suitable due to the reduction of the frictional resistances, is very complicated with respect to handling.
DE-OS 4,137,857 describes a hollow body. This prosthesis is compressed against the action of resetting spring forces to a cross section that is reduced versus the widened functional position, and kept in this position by means of a mountable covering. After the covering has been mounted, the prosthesis automatically widens to a cross section conforming to the functional position. The covering, which may be a meshwork approximately in the form of a round crocheting, extends over the entire length of the prosthesis and consists of at least one through-extending filament and one pull-up line. The prosthesis, which is kept in a radially compressed position by the covering, can be advanced, for example on a guide wire, or also rigidly received axially on the end of a probe or catheter.
Finally, an endoprosthesis is known, for which no documentation is available in the form of a published reference made from a memory alloy. This endoprosthesis is an oblong hollow body with a jacket that is broken many times and embodied in the way of a stretched metal.
This endoprosthesis automatically widens from a smaller insertion lumen to a larger lumen. However, this endoprosthesis has little flexibility and in any case potentially has the hazard of fatigue fractures when implanted via a joint. Not all of the struts forming the jacket are connected with each other in the corner points, and, in the implanted state, such struts may thus detach themselves from the vascular wall and protrude into such a wall.
Contrary to the above mentioned prior art, it is an object of the present invention to provide an endoprosthesis which, as compared to the stents known according to the state of the prior art, is more flexible and has superior strength and stability in the expanded state.
This object is achieved in accordance with the present invention in that the endoprosthesis is a hose-like netting produced from at least one elastic filament, such netting having the structure of a wire screen fence with mesh forming polygons, in which the filaments each grip around each other in their corner points in the direction of the meshes following one another in the direction of the longitudinal axis of the prosthesis.
An endoprosthesis of the invention, which may be self-expanding by means of a balloon catheter, is adaptable to the requirements in any given application in a simple way, and represents a flexible structure that is implantable without problems also in joint regions and then capable of following the movements of the joint of the patient without impediment. In particular, it is has been found that as compared to the prior art, such an endoprosthesis has an enhanced ratio between a small and a large radius in the widened position. This means that the insertion catheter to be inserted during implantation can be kept smaller than possible in connection with known prostheses.
It has been found that it is especially preferable if the hose-like netting forming the endoprosthesis comprises at least one through-extending filament, which is braided into a round shape, forming meshes. Alternatively, the endoprosthesis can be produced from an initially flat netting that is then rolled into a hose shape, whereby two longitudinal edges of the netting are then joined with each other by means of a longitudinal seam.
According to a particularly preferred embodiment of the invention, provision is made at the filaments loosely grip around each other, in each of the meshes adjacent to each other in the longitudinal direction of the prosthesis. In this manner, the prosthesis can be shortened from its maximum length so that the filaments will be abutting each other in the corner points of the meshes, by pushing the meshes together.
With such an embodiment, the endoprosthesis is one that can be changed in its length within predetermined limits, whereby in the case of maximum axial expanse, the filaments gripping around each other abut one another in the corner points of the meshes. On the other hand, in the case of a shortening, these filaments grip around each other with more or less axial play. The special advantage of such an embodiment of the prosthesis is that whenever the length is adjusted to a length smaller than the maximum length, no shortening occurs during widening because the material required for widening in the radial direction has not been made available by shortening the length, but is available through the filaments of the individual meshes which do not abut one another axially.
Furthermore, it has been found that it is desirable if the filaments are provided in the corner points of the meshes with interlocks engaging one another in an interlocking way. Such interlocks provide the prosthesis with a particularly pronounced strength in its widened condition.
The aforementioned interlocks may be depressions formed by compressing the filaments intersecting each other in the stretched condition of the prosthesis in the corner points to approximately the thickness of one filament. These depressions engaging each other in the stretched condition of the prosthesis in an interlocking way in their locking positions, thereby provide a form-closed lock in each corner point.
Instead of having the filaments loosely gripping around one another in the corner points of the meshes forming polygons, it is possible also to provide an embodiment in which, in the corner points of the meshes following each other in the direction of the longitudinal expanse of the prosthesis, the filament of each mesh is looped around the filament of the other mesh, forming an eye. Naturally, reducing the length of an endoprosthesis so formed by axial compression is limited, as compared to the embodiment with filaments that loosely grip around each other in the corner points.
According to another embodiment, provision is made that the filaments crossing each other in the corner points of the meshes are connected with each other, which means that the points of intersection are stabilized in this way. This naturally leads to a comparatively high stiffness of such an endoprosthesis. Stabilization can be realized in many different ways, for example by gluing, fusing or soldering of the filaments at the points of intersection. Also, at the points of intersection, the filaments can be enclosed by clips or joined with each other by clamping such filaments together.
An additional embodiment for achieving the object of the invention is one in which the endoprosthesis is a hose-like netting produced from elastic filaments, such netting having the structure of a mesh wire fence with meshes forming polygons, and that the meshes each have connection zones with two filaments twisted around each other, such zones of connection extending in the longitudinal direction of the prosthesis.
An endoprosthesis with the above features is characterized by a particularly pronounced strength and stability in the expanded widened state without impairing the flexibility of the hoselike netting.
In such an endoprosthesis, the connection zones comprising two filaments twisted around each other extend in the longitudinal direction of the prosthesis. According to a further embodiment, the connection zones can also extend along imaginary screw thread-like lines of an also imaginary cylinder jacket extending from the prosthesis, forming a helix structure. In this connection, the arrangement also may be selected in such a way that the helix structure is broken by changing the direction of successive meshes in a way such that with part of the meshes, the connection zones extending between such meshes extend at an angle relative to the zones of connection between other meshes, which leads to a structure as found in connection with xe2x80x9cfish scalesxe2x80x9d.
With such an endoprosthesis, meshes adjacent each other in the circumferential direction each can be formed by two filaments, and meshes following each other in the axial direction as well as meshes joined with each other in each case via a connection zone can be formed by the same two filaments. Alternatively, meshes disposed adjacent to each other in the circumferential direction each can be formed by two filaments, and the meshes disposed adjacent to each other axially and in the circumferential direction each can be formed by one of these filaments and another filament. Thus, the filaments participate in the axial direction and progressively from one mesh to the next in the formation of meshes disposed adjacent to each other in the circumferential direction, extending one after the other around the stent in the way of stairsteps. Such a formation of the stent has been found to be easily producible and to be advantageous with respect to its strength and stability in the widened state.
Another preferred embodiment of the invention is characterized in that in the corner points of the meshes disposed radially adjacent to each other, the filaments each are twisted around against each other with a winding in a way such that under axial tensile forces, the locks formed by the twistings become disengaged, and the prosthesis, when losing its radial bearing strength, undergoes a lengthwise expansion as well as a change in cross section, leading to a small lumen.
An endoprosthesis so formed can be advanced with a small cross section and corresponding longitudinal expanses without problems, for example in a blood vessel, by means of a suitable catheter, and subsequently brought into its functional position by radial widening associated with predetermined shortening.
Furthermore, with such an embodiment, the filaments can be provided with depressions engaging each other form-locked in the expanded state, by pressing them together in the zones of connection, such zones being twisted against each other, which, the widened state, results in superior locking and thus in greater radial bearing strength and stability.
According to another embodiment, provision is made that one filament extends in each case without twisting in the connection zones in the longitudinal direction of the prosthesis, and that the other filament is wound around this filament in the form of a spiral. Such an embodiment permits a limited sliding of the one filament along the straight-lined section of the other filament, and, in view of the spiral-like windings, also permits a compression and stretching of the one filament. This permits a superior adaptation of an endoprosthesis so formed within curved areas.
Another further embodiment includes a lock with at least one retaining bar, which extends in the longitudinal direction of the prosthesis and is solidly anchored in the netting with its one end, as well as provided on the other end with a hook for engaging a mesh. During radial widening of an endoprosthesis fitted with such a lock, the end of the retaining bar fitted with the hook slides across the meshes as the prosthesis is radially widened and the netting is shortened at the same time. The hook grips behind the filaments of the mesh, with the result that following the widening, the hose-like netting is prevented from radial compression in that any increase in length caused by a radial reduction is no longer possible.
Desirably, the retaining bar can extend along the hose-like netting on the outer side and, in the implanted state, thus can be received between a vascular wall and the hose-like netting. It is assured in this way that no impairment of the lumen will occur under any circumstances. However, the retaining bar may also extend through the meshwork of the netting in the way of a warp thread, which keeps the lumen free as well.
According to another preferred embodiment of the second variation of the invention, provision is made that the meshes comprise through-extending first filaments and second filaments connecting the first ones with each other. The second filaments are each wound around the first filaments by one mesh length and project at the end of the respective mesh to an adjacent first filament, and are wound again around the adjacent first filament again across one mesh length, and again project to another first filament at the end of the respective mesh. Thus, this type of mesh formation continues and the second filaments, upon winding around a first filament, each extend around an imaginary cylinder jacket of the endoprosthesis in a progressively, stair-step manner.
With a further development of the two embodiment variations explained above, it is desirable to provide for limiting the length of the stent, the hose-like netting is fitted with warps extending in the longitudinal direction of the stent, which warps may be connected with the filaments forming the meshes at least within the zone of the ends of the prosthesis. These warp threads may include textile filaments and may be arranged closely adjacent to each other in a way such that they form a jacket enclosing the stent.
According to a further embodiment of the last-mentioned feature, the warp threads may include biodegradable material and/or may be designed as medication depots, releasing medications in the course of their degradation. An example of such a biodegradable material is vegetable fiber or animal fiber. Other examples include polymers or their compounds poly-D, L-lactide; poly-D, L-lactide-co-trimethylene carbonate; or proteins.
According to yet another further embodiment, provision is made that the warp threads include extensible material such as textured textile threads. However, the warp threads may also include nonelastic material having a high density and proton number, which has been found to be particularly advantageous in connection with implantations under X-ray control because such a material absorbs X-rays to a high degree and is, therefore, highly visible in the X-ray image. Examples of such materials include titanium wire or stainless steel wire.
The filaments, whether first or second, can be made from biocompatable materials, such as polyamide fibers like nylon fibers or polyolefin fibers such as polyethylene fibers or polypropylene fibers. These fibers have a diameter which ranges between 0.01 mm and 1.0 mm.
Desirably, with the two embodiment variations discussed above, the ends of the filaments are bent off and joined with the netting at the face ends of the hose-like netting as well, in order to effectively avoid injury in the course of implantation, or in the implantation site. For example, the bentoff ends of the filaments may be braided in, glued, soldered or fused at the face ends of the hose-like netting, or also may be shaped as eyes.
According to another embodiment of these two variations, which is important as well, provision is made that the filaments forming the meshes of the hose-like netting are rounded off or flattened on the side facing the lumen, in order to obtain favorable properties of flow on the inside wall of a vessel receiving such an endoprosthesis. The term xe2x80x9clumenxe2x80x9d refers to a blood vessel.
Finally, it has been found to be desirable if in connection with these two embodiment variations, the filaments forming the netting are comprised by a super-elastic material, or a memory material, for example such as nitinol.
Within the framework of the present invention, both embodiment variations can be realized in the form of balloon-expandable or also self-expanding endorposthesis.
Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose several embodiments of the present invention. Is should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.